1. Field of the Invention
The present invention relates to an injector that controls opening/closing action of a needle by increasing/decreasing control pressure of a pressure control chamber through movement of a pressurizing piston driven by a piezoelectric actuator.
2. Description of Related Art
An injector using an electromagnetic valve as an actuator is commonly used. In order to realize a large flow rate and high response, an injector using a piezoelectric actuator with a large generative force and high response is proposed. For example, an injector described in patent document 1 (International Publication No. 2005/075811) has a piezoelectric actuator 100 that makes a displacement when voltage is applied thereto, a pressurizing piston 110 driven by the piezoelectric actuator 100, an outer sleeve 120 for slidably holding an outer periphery of the pressurizing piston 110, a pressure control chamber 130, internal pressure (oil pressure) of which increases/decreases according to the movement of the pressurizing piston 110, a needle 160 that is held inside a valve body 140 and that has a function to open/close an injection hole 150 and the like as shown in FIG. 6.
The pressure control chamber 130 is fluid-tightly defined by the pressurizing piston 110, the outer sleeve 120, the needle 160 and the valve body 140. If the voltage is applied to the piezoelectric actuator 100 and the pressurizing piston 110 is depressed downward in the drawing, the volume of the pressure control chamber 130 decreases and the internal pressure rises.
The internal pressure of the pressure control chamber 130 acts on a pressure receiving face 161 formed in the needle 160 to function as a valve opening force for biasing the needle 160 in a valve opening direction (upward direction in the drawing). If the valve opening force exceeds a valve-closing force (reaction force of a spring 170 and the like) biasing the needle 160 in a valve closing direction, the needle 160 lifts and opens the injection hole 150. Thus, the high pressure fuel supplied to an inside of the valve body 140 is injected into a combustion chamber 180 of the engine from the injection hole 150.
There is a possibility that an expansion-contraction direction of the piezoelectric actuator 100 inclines with respect to the axial direction of the injector when the fixation accuracy of the piezoelectric actuator 100 is low or because there is a variation among the products. In this case, since the above-mentioned injector is structured such that the piezoelectric actuator 100 and the pressurizing piston 110 contact each other in a plane, if the inclination arises in the expansion-contraction direction of the piezoelectric actuator 100, the driving force of the piezoelectric actuator 100 is transmitted to the pressurizing piston 110 in the inclined direction. Accordingly, the moving direction of the pressurizing piston 110 is inclined with respect to the axial direction, causing a distortion in sliding sections of the pressurizing piston 110 and the needle 160. As a result, there is a possibility that a malfunction of the needle 160 occurs.